A young gunman killed his mother and 25 other people, including 20 children, when he went on a shooting rampage inside a US school, before turning the gun on himself, in one of the deadliest such incidents witnessed in the country.

The shooter whose act of firing indisciminately at students and staff left the Connecticut city of Newton shocked and paralysed was earlier identified as 24-year-old Ryan Lanza.

The New York Post, the AP, and others later reported that the shooter’s name is Adam Lanza,
20, and not his elder brother Ryan Lanza. And it appears that the Ryan Lanza Facebook account
that was passed around immediately after the Newtown shooting belongs to
the suspect’s brother.

According to the New York Times, Lanza's mother was a teacher at the shool and he walked up to her classroom loaded with two 9mm handguns and wearing all black, and opened fire, killing her and 25 other adults and children.

He first shot and killed his mother and then shot 18 students in the classroom before killing himself inside the school.

The incident occurred at the Sandy Hook Elementary School in Newtown city of Connecticut state.

Connecticut police said "several fatalities" have been reported in the incident that sent crying children spilling into the school parking lot as frightened parents waited for a word on their kids.

Connecticut State Police lieutenant Paul Vance told reporters outside the school that the "shooter was deceased inside the building."

He said the shooting resulted in "several fatalities including students and staff."

The police has recovered a 9mm handgun from the scene. Officials said the shooter wore black combat dear and a military vest.

There was also some confusion initially about the number of shooters as some reports suggested two men were likely involved in the shooting episode.

Fox News quoted a law enforcement official as saying earlier that the shooter was believed to be a father of one of the students at the school.

The police however did not release information about the shooter and whether he was a parent or worked at the school.

Pictures showed panicked children, some of them crying, being led out to safety by their teachers.

US President Barack Obama was briefed by his top counter-terrorism advisor on the deadly shooting shortly after which he called the FBI Director and the Connecticut Governor.

Obama spoke to Connecticut Governor Dannel Malloy and expressed his condolences to the families of the victims. He promised that his administration would offer all help necessary to help deal with the tragedy.

Vance said the police received a 911 call at around 9:30 in the morning (local time) about the shooting. The school has been evacuated and the police is extensively searching the "every door and crack of the school" for information about the shooter and the motive.

A woman on the scene told CNN that "20 parents were told that their children are dead. It was aweful."

Vance said the scene has been secure and many agencies are working together to investigate the horrific incident.

"The President is receiving regular updates as more information becomes available about this incident," said White House Press Secretary, Jay Carney, at his daily news conference.

He said the FBI was supporting state law enforcement as well as local law enforcement, as they respond to and begin to investigate this incident.

Newtown is about 60 miles northeast of New York City and the school has about 600 students.

NBC Connecticut further reported that the entire school district was in lockdown and police and FBI agents were going room to room searching the school.

Such cases have prompted several politicians to seek a review of American gun laws. In August, a gunman went on a shooting spree in a Wisconsin gurdwara, claiming six lives.

In July, 12 people were killed and 38 injured in Colorado where a gunman opened fire at the premiere of the Batman movie The Dark Knight Rises.

"We are all stunned, shocked, and distraught by this tragic shooting, by this violent act, and by the loss of so many young children. Our hearts go out to the families and friends of the students, teachers, and educators killed and wounded in Newtown, Connecticut," said House Minority Leader, Nancy Pelosi.

"The entire nation will continue to stand as a source of support to this community in the days and weeks to come," Pelosi said.

US Senator Mark Begich said he was deeply saddened by the "deplorable" act of violence against children, who are the most vulnerable of individuals.

House Democratic Whip Steny Hoyer described the incident as a parent's worst nightmare and called it a "senseless tragedy".

"There can be no consolation other than to know that they have the heartfelt prayers and support of an entire nation," Hoyer said.